As one of pneumatic tires used on an icy and snowy road, a pneumatic tire as shown in FIG. 4, for example, is conventionally known. This pneumatic tire has a tread surface 21 provided with sipes 20, four main grooves 22 extending in the circumferential direction of the tire and lateral grooves 23 extending in the widthwise direction of the tire being disposed in the tread surface with proper adjustment, thereby improving on-ice performance and on-snow performance in a balanced manner (see a patent document 1, for example).
In recent years, due to global warming, opportunities when vehicles run on sherbet-like snowy road surfaces in snowfall areas have increased. It can not be said that a conventional tire used on an icy and snowy road as described above substantially satisfies on-snow performance on a snowy road surface including a sherbet-like snowy road surface; a technical approach for improving on-snow performance on a snowy road surface including a sherbet-like snowy road surface is required without deteriorating on-ice performance.
Patent Document 1: Japanese Patent Application Kokai Publication 2005-349970